Arrangements have been provided for improving smoothness in engine operation by having a balancer shaft that is driven from the crankshaft and which has a pair of counter weights on it, which balance certain vibrational forces of the engine. As noted, this type of arrangement is generally driven off of the crankshaft and frequently is interposed in the drive train to the camshaft or camshafts of the engine. The difficulty with this that the balancer shaft itself can present some torsional vibrations that can influence the engine operation. That is, the crankshaft vibrations can be transmitted to the balancer shaft and cause noise or decrease durability. Although torsional dampers can be employed, the previous interpositioning of the torsional damper in the balancer shaft drive has been avoided because of the fact that it can introduce variations in valve timing. If there is a torsional damper in the drive for the balancer shaft, the action of the torsional damper may also affect the timing between the crankshaft and the camshaft or camshafts.
It is, therefore, a principal object to this invention to provide an improved balancer shaft arrangement for an engine that can be interposed in the camshaft drive and will not affect the timing of the opening and closing of the valves.
A further problem in connection with the conventional type of balancer shaft mounting also deals with the journalling and loads on the bearings as may be best understood by reference to FIG. 1 which is a view showing a prior art type of balancer shaft, indicated generally by the reference numeral 11. The balancer shaft 11 has a main shaft portion that is formed integrally with a plurality of axially spaced bearings 12, 13, 14 and 15 by which the shaft 11 is journalled. A first balancer mass 16 is interposed between the bearings 12 and 13 and a second balancer mass 17 is interposed between the bearings 14 and 15.
The drive gear for the balancer shaft 11, indicated by the reference numeral 18, is also located adjacent the balancer mass 17 and between the two bearings 14 and 15. As a result of this construction, there is an uneven loading on the bearings 12, 13, 14 and 15 with those associated with the mass 17 and drive gear 18 being greater than those applied to the remaining bearings (12 and 13). This has resulted in the necessity for making the shaft of a greater diameter than desirable in order to reduce the loading and also requires enlargement of the bearings for the same purpose.
It is, therefore, a further object to this invention to provide an improved bearing arrangement for a balancer shaft of an engine wherein the loading on the individual bearings is significantly reduced.
A first feature of this invention is adapted to be embodied in an internal combustion engine having a crankshaft, at least one camshaft, a balancer shaft and a timing drive for driving the camshaft and the balancer shaft from the crankshaft. The balancer shaft has a drive member that is interposed in the timing drive and a torsional vibration damper that is interposed between this drive member and the balancer masses on the balancer shaft.
In accordance with another feature of the invention, a balancer shaft is provided that has at least offset balance masses formed thereon. The balancer shaft is also formed with integral bearings directly on opposite sides of each of the balance masses.